1. Field of the Invention
The present invention relates to a gas introduction pipe which can preferably used for a deposition apparatus or the like, and a method to produce magnetic recording medium in which oxygen gas is blown out by using the gas introduction pipe so as to form a magnetic layer.
2. Description of the Prior Art
In the field of video tape recorder, in order to obtain a high quality image, there is a strong request for a higher recording density. As a magnetic recording medium to answer this request, there has been proposed a so-called metal magnetic thin film type magnetic recording medium having a magnetic layer formed by applying a metal magnetic material directly onto a non-magnetic support body by way of plating and vacuum thin film formation technique (vacuum deposition, sputtering, ion plating method, and the like).
This metal magnetic thin film type magnetic recording medium has various advantages such as an excellent coercive force, an excellent rectangular ratio, and an excellent electromagnetic conversion characteristic in a short wavelength band. Such a magnetic recording medium also enables to form the magnetic layer as a thin film with a high filling density of a magnetic material because there is not need of mixing a binder or other non-magnetic material in the magnetic layer such as in a painting-type magnetic recording medium.
Especially, a deposition-type magnetic tape (deposited magnetic tape) having a magnetic layer formed by vacuum deposition method has a high production efficiency and a stable characteristic and already used in practice.
The deposition for forming the magnetic layer in the aforementioned deposited tape is carried out by a deposition apparatus-including a vacuum chamber, a can roll for guiding a non-magnetic support body, a magnetic material as a deposition source, heating means for heating the deposition source, and the like.
In this deposition apparatus, the magnetic material serving as the deposition source is evaporated into a metal vapor by electron ray radiation or the like, so that the metal vapor is deposited to form a film on a non-magnetic support body which runs along an outer circumference of the can roll.
Here, the metal magnetic thin film thus formed has a magnetic characteristic which is affected by an incident angle of the metal particles coming onto the non-magnetic support body. In order to control the incident angle of this metal vapor, a shutter is normally provided in the vicinity of the can roll so as to cover a predetermined area of the support body.
Moreover, in order to improve the magnetic characteristic of the magnetic layer such as the coercive force and the saturation magnetic flux density, it is normal to use an oxygen gas introduction pipe having a slit-shaped blowoff opening along the width direction of the non-magnetic support body, so as to oxidize the metal vapor by the oxygen gas supplied from this slid. This oxygen gas introduction pipe is attached to the shutter cooled by water, so as to prevent deformation by a high temperature vapor.
FIG. 1 and FIG. 2 show an oxygen gas introduction pipe 100 including a gas supply pipe 101 for supplying an oxygen gas from outside, and a gas flow block 103 having a flow passage 102 of the oxygen gas supplied from this gas supply pipe 101. This gas flow block 103 has an upper cover 104 (FIG. 2) and an introduction pipe body 105 which are matched to each other via a predetermined clearance. The upper cover 104 and the introduction pipe body 105 are connected in this gas flow block 103 with a plurality of bolts 106.
Moreover, the introduction pipe body 105 includes a cooling circuit 107 formed therein. This cooling circuit 107 is supplied with a cooling water from a cooling water flow-in pipe 108 (FIG. 1) attached to the oxygen gas introduction pipe 100.
Furthermore, in this oxygen gas introduction pipe 100, a spacer (not depicted) is inserted between the upper cover 104 (FIG. 2) and the introduction pipe body 105 so as to define the clearance between the upper cover 104 and the introduction pipe body 105 to be a predetermined width.
Moreover, in this oxygen gas introduction pipe 100, a blowoff opening 109 for blowing off oxygen gas is defined by the clearance between the upper cover 104 and the introduction pipe body 105. An oxygen gas port 110 is also formed as a hollow space defined by the upper cover 104 and the introduction pipe body 105 which are matched to each other.
In the deposition apparatus using the oxygen gas introduction pipe 100 having the aforementioned configuration, when forming a magnetic layer on a non-magnetic support body, oxygen gas is blown out from the oxygen gas introduction pipe 100 to the metal vapor. The metal vapor is oxidized in a predetermined quantity and accumulated on the non-magnetic support body.
By the way, the aforementioned oxygen gas introduction pipe 100 when used in a deposition apparatus for example, is subjected to a high temperature atmosphere such as about 1000 to 1200 C. For this, the oxygen gas introduction pipe 100 is provided with the cooling circuit 107 in the introduction pipe body 105. Consequently, there will hardly be caused deformation of the introduction pipe body 105 by heat.
However, this oxygen gas introduction pipe 100 is not provided with means for cooling the upper cover 104, which is often deformed by heat. Moreover, in this oxygen gas introduction pipe 100, the upper cover 104 and the introduction pipe body 105 are fixed with a plurality of bolts 106. If the upper cover 104 is deformed as has been described above, the deformation is small in the vicinity of the bolts 106 and large in the portion between the bolts 106. Thus, in the oxygen gas introduction pipe 100, the deformation occurs not in a uniform manner over the upper cover 104.
Thus, if the upper cover 104 is deformed unevenly by heat, there arises irregularities in the width of the blowoff opening 109. As a result, the oxygen gas introduction pipe 100 is disabled to blow off the oxygen gas uniformly from the blowoff opening 109.
For this, if this oxygen gas introduction pipe 100 is used for forming a metal magnetic thin film, oxidation lacks in uniformity in the width direction of the blowoff opening 109, which in turn brings about an uneven film thickness in the width direction. As a result, the metal magnetic thin film obtained has irregularities, making unstable the electromagnetic conversion characteristic.
On the other hand, when this oxygen gas introduction pipe 100 is used for a deposition apparatus, the deposition material may adhere to the vicinity of the blowoff opening 109. In such a case, the material is physically peeled off from the vicinity of the blowoff opening 109 of the oxygen gas introduction pipe 100.
In the conventional oxygen gas introduction pipe 100, the physical peeling off of the material often damages the vicinity of the blowoff opening 109. This also makes uneven the slit width of the blowoff opening 109 in the oxygen gas introduction pipe 100. As a result, it becomes impossible to blow off the oxygen gas in a uniform manner. In this case, similarly as has been described above, the oxygen gas introduction pipe 100 results in forming a metal magnetic thin film having an unstable electromagnetic conversion characteristic.
In the conventional oxygen gas introduction pipe 100, when deformation by heat or damage is caused as has been described above, the upper cover 104 and the introduction pipe body 105 should be entirely replaced with new ones. Thus, in order to maintain the oxygen gas blowoff quantity constant and uniform, the conventional oxygen gas introduction pipe 100 requires overall replacement of components.
Thus, the conventional oxygen gas introduction pipe 100 has a problem that deformation and damage caused require replacement of components, which increases the maintenance costs.